Fertilization is a complex but highly ordered sequence of gamete interactions which begins with approximation of sperm and egg and culminates with the onset of cleavage. Freshly ejaculated sperm of most mammalian species examined are not immediately capable of fertilizing eggs but acquire that capacity while residing in the female reproductive tract. This project has as its long-term goal identification and understanding of the discrete sequence of changes in sperm which endow them with the capacity to fertilize eggs, and of the discrete interactions between "capacitated" sperm and eggs which result in fertilization of the egg. Species used in the project include golden hamsters, guinea-pigs, mice, gerbils and bush babies. The approach is in vitro. Current studies are directed toward the time-course of normal and degenerative acrosome reactions in capacitating media, the mode and function(s) of the normal acrosome reaction, conditions which support occurrence of the normal reaction in vitro, and toward establishment of the suitability of the prosimian, Galago senegalensis for laboratory studies of fertilization.